The embodiment of the present invention relates to a silicon (Si) sputtering target, and in particular relates to a sputtering target formed from monocrystalline silicon which is free from cracking and exhibits high sputtering performance even when high power is input.
Silicon is the basic material of modern semiconductor electronic devices, and many of the semiconductor electronic devices are formed using silicon-based materials excluding those that are used for special purposes. Silicon is also broadly used in the form of pure silicon or a silicon compound not only as a substrate material on which various elements and devices are formed, but also as a material for partially forming various constituent elements in the devices.
When silicon or a silicon compound is formed as a constituent element other than a bulk-shaped substrate, such silicon or silicon compound in the form of a thin film having a predetermined thickness is often used in an area of a predetermined range. For example, a polycrystalline silicon film is used as an electrode or an active layer of semiconductor devices or in solar cells; a silicon oxide film is used as a gate insulation film or an element isolation layer of a field effect transistor (FET) structure or as an optical adjustment film; and a silicon nitride film is used as a device protective layer for preventing the diffusion of water and nitrogen, and as a mask for use upon selectively oxidizing silicon.
This kind of silicon or silicon compound thin film is produced by suitably selecting the thin film forming method according to usage and purpose. Conventionally, the chemical vapor deposition (CVD) method was often used in light of superior characteristics such as deposition rate and step coverage. Nevertheless, in recent years, the sputtering method is also being used in cases where a silicon film or a silicon compound film is formed as a part of a composite device based on a combination with a material having low heat resistance properties, and in terms of the superiority of process for usages in which high purity and strict film thickness control are required.
When forming a silicon film or a silicon compound film based on the sputtering method, a sputtering target formed from a silicon material is required. In relation to a silicon sputtering target, as described in Patent Documents 1 and 2, known is a target formed from a silicon sintered body which is obtained by subjecting powdered silicon grains to densification and sintering. With this kind of sintered target, there are problems of impurity inclusion and oxidation during the pulverization and sintering of the raw material powder. As a type capable of resolving the foregoing problems, known is a sputtering target which uses polycrystalline silicon produced via the melting method as described in Patent Document 3.
As described above, the technology of silicon materials has been established as a result of numerous means and findings for producing a high purity monocrystal as a substrate material of semiconductor devices being accumulated over the years. Especially in recent years, the production of a large diameter silicon ingot having a diameter of 300 mm, and even 450 mm, has been realized. In line with this, the use of monocrystalline silicon, in which the production technology of high purity products has been established, as a sputtering target is being considered. Patent Document 4 describes the use of a monocrystalline silicon ingot having a diameter of 300 mm or more as a sputtering target.
Nevertheless, when monocrystalline silicon is actually used as a sputtering target, as also indicated in Patent Document 2, it is known that crystalline silicon cracks easily and there are issues regarding mechanical strength. The conventional knowledge regarding the strength of monocrystalline silicon is described in Patent Documents 5 and 6. Patent Document 5 describes that a wafer-shaped silicon in which the plane orientation of the main surface is {111} by subjecting the main surface of a wafer to be inclined at a predetermined angle from a {111} plane in order to prevent the occurrence of slippage due to thermal stress during the production process.
Meanwhile, when using monocrystalline silicon as a large-area sputtering target, the {100} plane is often used as the sputter surface. When growing monocrystalline silicon having a large diameter, this is limited to <100> axis crystals in which the glide dislocation of seed crystals can be eliminated easily. In other crystal orientations, the diameter of the monocrystalline silicon needs to be narrowed down considerably during the necking process, because a large product with a large diameter and heavy weight cannot be pulled. And conventionally, when obtaining a large-area silicon sputtering target, the target was cut into a disk shape on a plane that is perpendicular to the axis direction of the <100> monocrystalline ingot pulled with the CZ method, and the {100} plane was used as the sputter surface of the target.
With regard to a silicon wafer in which the main surface is the {100} plane, Patent Document 6 describes the problem of the wafer cracking along the {110} plane as the cleaved surface that is perpendicular to the {100} plane during the production process. In order to solve the problem, Patent Document 6 describes a wafer with increased strength that is resistant to cracks by causing the main surface of the wafer to be a plane that is inclined at a predetermined inclination angle relative to all equivalent <110> orientations. Nevertheless, with regard to monocrystalline silicon having a certain degree of thickness such as with a sputtering target, there is no disclosure as to the specific level that the strength can be improved by actually inclining the orientation to what degree.
It is known that, in the field of silicon wafers, types in which the main surface of the wafer is of a slightly inclined plane by being inclined at a predetermined angle from a generally used low-index plane such as {100} or {111} as disclosed in Patent Documents 7 to 10 for the purpose of inhibiting defects, improving flatness and improving impurity gettering power of an epitaxial layer to be grown on the wafer. However, these documents do not cause the main surface to be a plane inclined relative to the low-index plane from the perspective related to the strength of monocrystalline silicon, let alone sputter characteristics.